US7995433B2 - Optical head apparatus and optical disc apparatus - Google Patents

Optical head apparatus and optical disc apparatus Download PDF

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US7995433B2
US7995433B2 US12/601,144 US60114408A US7995433B2 US 7995433 B2 US7995433 B2 US 7995433B2 US 60114408 A US60114408 A US 60114408A US 7995433 B2 US7995433 B2 US 7995433B2
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light
order diffracted
information recording
recording surface
diffracted light
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US20100149936A1 (en
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Hironori Nakahara
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0901—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following only
    • G11B7/0903—Multi-beam tracking systems
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0901—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following only
    • G11B7/0906—Differential phase difference systems
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0943—Methods and circuits for performing mathematical operations on individual detector segment outputs
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage
    • G11B2007/0013—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage for carriers having multiple discrete layers

Definitions

  • the present invention relates to an optical head apparatus irradiating a multi-layer optical disc having a plurality of information recording surfaces with laser light and detecting reflected light and an optical disc apparatus having the optical head apparatus.
  • an optical disc 10 such as a CD (compact disc), DVD (digital versatile disc), and BD (Blu-ray disc)
  • a playback-only optical disc having a spiral recording track TR which is formed by rows of pits TB with a track pitch TP on an information recording surface as shown in FIG. 1
  • a write-once or rewritable type optical disc having a spiral recording track TR onto which recording marks TM are written with a track pitch TP on an information recording surface as shown in FIG. 2 .
  • An optical disc apparatus has an optical head apparatus irradiating the optical disc 10 with laser light and detecting reflected light of the laser light and a servo circuit causing a light-collected spot at which the light is collected on the information recording surface of the optical disc to follow the recording track TR.
  • a photodetector 19 of a conventional optical head apparatus has a main-beam light-receiving unit 19 M for detecting zero-order diffracted light (main beam) which is reflected by the optical disc, and sub-beam light-receiving units 19 S 1 and 19 S 2 for detecting positive and negative first-order diffracted light (sub beams) which is reflected by the optical disc.
  • the main-beam light-receiving unit 19 M is divided in four sections and includes divisional light-receiving elements 19 a , 19 b , 19 c , and 19 d .
  • the sub-beam light-receiving unit 19 S 1 is divided in two sections and includes divisional light-receiving elements 19 e and 19 f .
  • the sub-beam light-receiving unit 19 S 2 is divided in two sections and includes divisional light-receiving elements 19 g and 19 h .
  • Patent document 1 Japanese Patent Kokai Publication No. 61-94246
  • Patent document 2 Japanese Patent Kokai Publication No. 2005-346882
  • an intensity ratio between the main beam and the sub beam is about 10 to 1.
  • the following problem occurs when recording/reproducing on/from a dual-layer optical disc is performed.
  • interlayer stray light unnecessary reflected light from the other information recording surface which is not the access-target information recording surface enters a divisional light-receiving element of a photodetector in the optical head apparatus.
  • Patent document 2 a phenomenon that interlayer stray light causes a tracking error signal inaccurate is avoided through the use of a signal of a light-receiving device disposed near a sub-beam light-receiving unit.
  • a phenomenon that interlayer stray light causes a tracking error signal inaccurate is avoided through the use of a signal of a light-receiving device disposed near a sub-beam light-receiving unit.
  • light-receiving devices and calculation circuits are added and consequently, another problem occurs that the configuration of the optical head apparatus is complicated.
  • the present invention is made to solve the problems of the conventional art and its object is to provide an optical head apparatus and an optical disc apparatus which can reduce undesirable influence on a differential push-pull signal caused by interlayer stray light, without making the configuration complicated.
  • an optical head apparatus irradiating a multi-layer optical disc having a plurality of information recording surfaces with laser light and detecting reflected light of the laser light, includes: a laser light source; a diffraction means splitting laser light which is emitted from the laser light source into zero-order diffracted light, positive-first-order diffracted light, and negative-first-order diffracted light; a photodetector; and an optical system means collecting the zero-order diffracted light, the positive-first-order diffracted light, and the negative-first-order diffracted light, on an access-target information recording surface out of the plurality of information recording surfaces, and guiding on the photodetector, reflected light of the zero-order diffracted light, reflected light of the positive-first-order diffracted light, and reflected light of the negative-first-order diffracted light by the access-target information recording surface; wherein: the optical system means includes an adjusting means moving a light-collected position of the zero-
  • another optical head apparatus irradiating a multi-layer optical disc having a plurality of information recording surfaces with laser light and detecting reflected light of the laser light, includes: a laser light source; a diffraction means splitting laser light which is emitted from the laser light source into zero-order diffracted light, positive-first-order diffracted light, and negative-first-order diffracted light; a photodetector; and an optical system means collecting the zero-order diffracted light, the positive-first-order diffracted light, and the negative-first-order diffracted light, on an access-target information recording surface out of the plurality of information recording surfaces, and guiding reflected light of the zero-order diffracted light, reflected light of the positive-first-order diffracted light, and reflected light of the negative-first-order diffracted light by the access-target information recording surface, on the photodetector; wherein: the optical system means includes an adjusting means moving a light-collected position of the zero-
  • the apparatus is configured so as to make a length in the y-direction U y of the divisional light-receiving element of the sub-beam light-receiving unit be N 2 times, N 2 being an integer, as long as a length in the y-direction T y of one period of an interference fringe formed on the divisional light-receiving element by reflected light from an information recording surface other than an access-target information recording surface, and thereby it is possible to reduce influence of interlayer stray light on a sub-beam push-pull signal. Therefore, an effect to improve accuracy of tracking control can be achieved without making a configuration of the apparatus complicated.
  • FIG. 1 is a diagram showing a plan view of a playback-only optical disc and recording tracks.
  • FIG. 2 is a diagram showing a plan view of a write-once or rewritable type optical disc and recording tracks.
  • FIG. 3 is a plan view showing divisional light-receiving elements of a conventional optical head apparatus.
  • FIG. 4 is a diagram schematically showing a cross sectional view of a dual-layer optical disc.
  • FIG. 5 is a block diagram showing a configuration of an optical disc apparatus according to a first embodiment of the present invention.
  • FIG. 6A and FIG. 6B relate to the optical head apparatus according to the first embodiment of the present invention:
  • FIG. 6A is a diagram showing an x-direction which is a tangential direction of a recording track on an optical disc and a y-direction which is a radial direction of the optical disc;
  • FIG. 6B is a diagram schematically showing a configuration of an optical system of an optical head apparatus according to the first embodiment of the present invention.
  • FIG. 7 is a plan view showing an arrangement and shapes of divisional light-receiving elements of a photodetector in the optical head apparatus according to the first embodiment.
  • FIG. 8A is a diagram showing a case that a second information recording surface is an access target and a first information recording surface is not an access target; and FIG. 8B is a diagram showing a shape of a spot of interlayer stray light of a main beam from the first information recording surface on the photodetector.
  • FIG. 9A is a diagram showing a case that the first information recording surface is an access target and the second information recording surface is not an access target; and FIG. 9B is a diagram showing a shape of a spot of interlayer stray light of a main beam from the second information recording surface on the photodetector.
  • FIG. 10 is a diagram showing an interference fringe on divisional light-receiving elements, by the interlayer stray light of the main beam and interlayer stray light of sub beams, from the first information recording surface, in the case of FIG. 8 .
  • FIG. 11 is a diagram showing an interference fringe on divisional light-receiving elements of an optical head apparatus and a waveform of a push-pull signal in a first sub-beam light-receiving unit according to an example for comparison.
  • FIG. 12 is a diagram showing the divisional light-receiving elements of the optical head apparatus according to the first embodiment.
  • FIG. 13 is a diagram showing an interference fringe on the divisional light-receiving elements and a waveform of a push-pull signal in a first sub-beam light-receiving unit, in the case of FIG. 8 .
  • FIG. 14 is a diagram showing an interference fringe on the divisional light-receiving elements, by the interlayer stray light of the main beam and the interlayer stray light of the sub beams, from the second information recording surface, in the case of FIG. 9 .
  • FIG. 15 is a diagram showing the interference fringe on the divisional light-receiving elements and a waveform of a push-pull signal in a first sub-beam light-receiving unit, in the case of FIG. 9 .
  • FIG. 16 is a plan view showing divisional light-receiving elements of a photodetector in the optical head apparatus according to the second embodiment of the present invention and a length in a y-direction of an interference fringe by interlayer stray light.
  • FIG. 17A is a plan view showing divisional light-receiving elements and an interference fringe by interlayer stray light in the example for comparison
  • FIG. 17B is a plan view showing divisional light-receiving elements and an interference fringe by interlayer stray light in another example for comparison
  • FIG. 17C is a plan view showing divisional light-receiving elements and an interference fringe by interlayer stray light in the second embodiment.
  • FIG. 18A , FIG. 18B , and FIG. 18C are diagrams showing influence of an interference fringe by interlayer stray light on a sub-beam push-pull signal in the optical head apparatus of the example for comparison which has the photodetector of FIG. 17A .
  • FIG. 19A , FIG. 19B , and FIG. 19C are diagrams showing influence of an interference fringe by interlayer stray light on a sub-beam push-pull signal in the optical head apparatus of the other example for comparison which has the photodetector of FIG. 17B .
  • FIG. 20A , FIG. 20B , and FIG. 20C are diagrams showing that an interference fringe by interlayer stray light has no influence on a sub-beam push-pull signal in the optical head apparatus according to the second embodiment.
  • FIG. 4 is a cross sectional view schematically showing a configuration of a dual-layer optical disc 10 .
  • the optical disc 10 includes a substrate 10 a , a first information recording surface 10 b formed on the substrate 10 a , an intermediate layer 10 e formed on the first information recording surface 10 b , a second information recording surface 10 d formed on the intermediate layer 10 c , and a cover layer 10 e formed on the second information recording surface 10 d .
  • the disc is 1.2 mm thick
  • the intermediate layer 10 c is 25 ⁇ m thick
  • the cover layer 10 e is 75 ⁇ m thick.
  • Laser light (a dot-dash line) which includes zero-order diffracted light 31 (a main beam), positive-first-order diffracted light 32 (a sub beam) and negative-first-order diffracted light 33 (a sub beam), as described below, enters from a disc surface 10 f and is collected on the first information recording surface 10 b or the second information recording surface 10 d .
  • the laser light being blue-violet laser with a wavelength of 405 nm, is collected by an objective lens of NA 0.85 which is not shown in the drawings.
  • Laser light 41 , 42 , and 43 being reflected at the first information recording surface 10 b or the second information recording surface 10 d are detected by a photodetector described below.
  • FIG. 5 is a block diagram schematically showing a configuration of the optical disc apparatus according to the first embodiment of the present invention.
  • the optical disc apparatus according to the first embodiment includes a spindle motor 11 rotating a turntable (not shown in the drawing) onto which the optical disc 10 is mounted, an optical head apparatus 21 irradiating the optical disc 10 with laser light and detecting reflected light of the laser light, a matrix circuit 24 , a signal reproducing circuit 25 , a servo circuit 26 , a spindle controlling circuit 12 , a laser controlling circuit 27 , a thread controlling circuit 23 , and a controller 28 formed by a microcomputer.
  • the spindle motor 11 rotates the turntable onto which the optical disc 10 is mounted.
  • the spindle controlling circuit 12 controls an operation of the spindle motor 11 .
  • the optical head apparatus 21 irradiates the multi-layer optical disc 10 having a plurality of information recording surfaces with laser light and detects reflected light of the laser light.
  • a thread mechanism 22 moves the optical head apparatus 21 in a radial direction of the optical disc 10 and thereby makes it possible to read information recorded in a desired position in the radial direction of the optical disc 10 by the optical head apparatus 21 .
  • the thread controlling circuit 23 controls an operation of the thread mechanism 22 .
  • the matrix circuit 24 having a matrix calculating/amplifying circuit and the like, performs a matrix calculation on output signals from a plurality of divisional light-receiving elements of a photodetector in the optical head apparatus 21 and produces a necessary signal.
  • the matrix circuit 24 produces, for example, a high-frequency reproduction signal, a focus error signal, a tracking error signal for servo control, and the like.
  • the reproduction signal output from the matrix circuit 24 is supplied to the signal reproducing circuit 25 , and the focus error signal and the tracking error signal are supplied to the servo circuit 26 .
  • the signal reproducing circuit 25 performs binarization of the reproduction signal and recovered clock generating processing and the like, and produces reproduction data.
  • the decoded reproduction data is transferred to a host device which is not shown in the drawings.
  • the host device is an AV system device, a personal computer or the like, for example.
  • the servo circuit 26 On the basis of the focus error signal and the tracking error signal supplied from the matrix circuit 24 , the servo circuit 26 produces a focus servo driving signal and a tracking servo driving signal, and causes the optical head apparatus 21 to perform a servo operation. That is, the servo circuit 26 produces a focus driving signal and a tracking driving signal in accordance with the focus error signal and the tracking error signal, and drives a focus coil and a tracking coil of the optical head apparatus 21 .
  • Such a configuration produces a tracking servo loop and a focus servo loop, which include the optical head apparatus 21 , the matrix circuit 24 and the servo circuit 26 .
  • the laser controlling circuit 27 controls intensity of laser which is emitted by the laser light source of the optical head apparatus 21 .
  • the controller 28 controls operations of a servo system and a reproduction system, in accordance with a command from the host device.
  • FIG. 6A and FIG. 6B relate to the optical head apparatus 21 according to the first embodiment of the present invention:
  • FIG. 6A is a diagram showing an x-direction which is a tangential direction of a recording track on the optical disc 10 and a y-direction which is a radial direction of the optical disc 10 ;
  • FIG. 6B is a diagram schematically showing a configuration of an optical system of the optical head apparatus 21 according to the first embodiment.
  • the x-direction on the optical disc 10 in FIG. 6A corresponds to an x-direction on a photodetector 9 .
  • the optical head apparatus 21 irradiates the multi-layer optical disc 10 having the plurality of information recording surfaces with the laser light 31 , 32 , and 33 , and detects the reflected light 41 , 42 , and 43 of the laser light.
  • the optical head apparatus 21 includes: a laser light source (semiconductor laser) 1 ; a diffraction means having a diffraction grating 2 splitting laser light 30 which is emitted from the laser light source 1 into the zero-order diffracted light 31 (main beam), the positive-first-order diffracted light 32 (sub beam) and the negative-first-order diffracted light 33 (sub beam); a polarization beam splitter 3 ; a collimator lens 4 ; a quarter-wave plate 5 ; an objective lens 6 ; an objective lens actuator 7 driving the objective lens 6 in the focus direction and the tracking direction; a cylindrical lens 8 ; and the photodetector 9 detecting the reflected laser light 41 , 42 , and 43 by the optical disc 10 .
  • a laser light source semiconductor laser
  • a diffraction means having a diffraction grating 2 splitting laser light 30 which is emitted from the laser light source 1 into the zero-order diffracted light 31 (main beam), the positive-
  • FIG. 7 is a plan view showing an arrangement and shapes of the divisional light-receiving elements of the photodetector 9 in the optical head apparatus 21 according to the first embodiment.
  • the photodetector 9 includes a main-beam light-receiving unit 9 M detecting the zero-order diffracted light 41 (main beam) reflected at the optical disc 10 , a sub-beam light-receiving unit 9 S 1 detecting the positive-first-order diffracted light 42 (sub beam) reflected at the optical disc 10 , and a sub-beam light-receiving unit 9 S 2 detecting the negative-first-order diffracted light 43 (sub beam) reflected at the optical disc 10 .
  • the main-beam light-receiving unit 9 M is equally divided in four sections by a division line in an x-direction and a division line in a y-direction and includes divisional light-receiving elements 9 a , 9 b , 9 c , and 9 d .
  • the sub-beam light-receiving unit 9 S 1 is divided in two sections by a division line in the x-direction and includes two divisional light-receiving elements 9 e and 9 f which are arranged in the y-direction.
  • the sub-beam light-receiving unit 9 S 2 is divided in two sections by a division line in the x-direction and includes two divisional light-receiving elements 9 g and 9 h which are arranged in the y-direction.
  • detection signal values of the divisional light-receiving elements 9 a , 9 b , 9 c , 9 d , 9 e , 9 f , 9 g , and 9 h are A, B, C, D, E, F, G, and H, respectively
  • a differential push-pull error signal (tracking signal) TES is expressed by the following equation:
  • the light emitted from the laser light source 1 firstly passes through the diffraction grating 2 .
  • the diffraction grating 2 produces the positive and negative first-order diffracted light 32 and 33 (sub beams) forming side spots for generating a tracking error signal, and then the polarization beam splitter 3 reflects the positive and negative first-order diffracted light 32 and 33 as well as the zero-order diffracted light 31 (main beam) forming a main spot.
  • the main beam 31 and the sub beams 32 and 33 are collimated at the collimator lens 4 , pass through the quarter-wave plate 5 , and then are collected by the objective lens 6 on the first information recording surface 10 b or the second information recording surface 10 d of the optical disc 10 .
  • the collimator lens 4 changes its position, by a mechanism to change the position in an optical-axis direction being parallel to a laser-light traveling direction, for compensating spherical aberration caused by a thickness error in the cover layer 10 e of the optical disc 10 .
  • the objective lens 6 moves in the focus direction and the tracking direction by the objective lens actuator 7 .
  • Reflected light from the optical disc 10 passes through the objective lens 6 , the quarter-wave plate 5 and the collimator lens 4 , reaches the polarization beam splitter 3 , and then transmits the polarization beam splitter 3 .
  • the optical head apparatus 21 according to the first embodiment in which an astigmatism method is used for the focus error signal and a differential push-pull method is used for the tracking error signal the light which has transmitted the polarization beam splitter 3 passes through the cylindrical lens 8 and enters the photodetector 9 for detecting a servo error signal and a reproduction signal and then photoelectric conversion is performed.
  • the focus error signal and the tracking error signal according to the differential push-pull method are determined.
  • ⁇ is about 32 degrees.
  • the divisional light-receiving element is a quadrilateral having a side of 150 ⁇ m
  • the power of an optical system is fourteen times and an interlayer interval is 25 ⁇ m
  • the intensity ratio ⁇ of the interlayer stray light can be calculated as the following equation:
  • the intensity ratio of the interlayer stray light is 3.7% and the interlayer stray light has little influence.
  • the intensity of the sub beam is 1/10 of that of the main beam
  • the intensity ratio of the interlayer stray light is accordingly 37%, i.e. ten times, and it cannot be ignored.
  • FIG. 8A is a diagram showing a case that the second information recording surface 10 d of the optical disc 10 is an access target and the first information recording surface 10 b is not an access target.
  • FIG. 8B is a diagram showing a shape of a spot of the interlayer stray light of the main beam from the first information recording surface 10 b on the photodetector 9 .
  • the spot of the interlayer stray light 51 of the main beam from the first information recording surface 10 b which is not the access target is substantially circle-shaped.
  • FIG. 9A is a diagram showing a case that the first information recording surface 10 b of the optical disc 10 is an access target and the second information recording surface 10 d is not an access target.
  • FIG. 9B is a diagram showing a shape of a spot of the interlayer stray light of the main beam from the first information recording surface 10 d on the photodetector 9 . As shown in FIG. 9B , in the case that the first information recording surface 10 b of the optical disc 10 is the access target, when a light-collected spot is irradiated, the spot of the interlayer stray light 61 of the main beam from the second information recording surface 10 d which is not the access target is oval-shaped.
  • FIG. 10 is a diagram showing an interference fringe on the divisional light-receiving elements by the interlayer stray light of the main beam from the first information recording surface 10 b and interlayer stray light of the sub beams, in the case of FIG. 8 . As shown in FIG.
  • the interlayer stray light 51 of the main beam from the first information recording surface 10 b which is not the access target and interlayer stray light 52 and 53 of the sub beams form an interference fringe 54 in a striped pattern that bright bands and dark bands extending in the x-direction are arranged one after the other in the y-direction, on the photodetector 9 .
  • a length (width) in the y-direction of one period of the interference fringe 54 is T y ⁇ m.
  • a parallel direction to the interference fringe 54 is the x-direction and an orthogonal direction to the interference fringe is the y-direction.
  • a calculation of (E ⁇ F) is performed, and on detected signals G and H by the divisional light-receiving elements 9 g and 9 h of the sub-beam light-receiving unit 9 S 2 , a calculation of (G ⁇ H) is performed.
  • a signal (E ⁇ F) and a signal (G ⁇ H) are detected under the influence of the interference fringe by the interlayer stray light.
  • FIG. 11 is a diagram showing an interference fringe on the divisional light-receiving elements of the photodetector in the optical head apparatus and a waveform of a push-pull signal Vef at the divisional light-receiving elements 9 e and 9 f of the sub-beam light-receiving unit 9 S 1 , in an example for comparison.
  • a relative slope of the optical disc 10 to the objective lens 6 slightly changes.
  • the interference fringe by the stray light of the main beam and the stray light of the sub beam vertically moves in the y-direction in accordance with the slight change in relative slope.
  • FIG. 11 is a diagram showing an interference fringe on the divisional light-receiving elements of the photodetector in the optical head apparatus and a waveform of a push-pull signal Vef at the divisional light-receiving elements 9 e and 9 f of the sub-beam light-receiving unit 9 S 1 , in an example for comparison.
  • servo performance is deteriorated and further a servo error is caused.
  • FIG. 12 is a diagram showing the divisional light-receiving elements of the photodetector 9 in the optical head apparatus 21 according to the first embodiment. As shown in FIG.
  • FIG. 13 is a diagram showing an interference fringe on the divisional light-receiving elements 9 e and 9 f and a waveform of a push-pull signal Vef in the sub-beam light-receiving unit 9 S 1 , in the case of FIG. 8 .
  • N 1 being a positive integer
  • the differential push-pull signal TES is not influenced by the interference fringe by the interlayer stray light.
  • the signal (E ⁇ F) and the signal (G ⁇ H) calculated from the signals E, F, G, and H detected by the divisional light-receiving elements 9 e , 9 f , 9 g , and 9 h of the sub-beam light-receiving units maximally change and influence on the differential push-pull signal TES is the maximum.
  • FIG. 14 is a diagram showing an interference fringe on the divisional light-receiving elements, by the interlayer stray light of the main beam from the second information recording surface 10 d and the interlayer stray light of the sub beam, in the case of FIG. 9 .
  • the interference fringe extends in an oblique direction being sloped to the x-direction.
  • FIG. 15 is a diagram showing an interference fringe on the divisional light-receiving elements and a waveform of a push-pull signal of the sub-beam light-receiving unit 9 S 1 , in the case of FIG. 9 .
  • the drawing shows how the interference fringe shifts if the lengths in the y-direction of the divisional light-receiving elements 9 e and 9 f for detecting the sub beam are T y ⁇ N 1 and the signal (E ⁇ F) which is calculated from the signals E and F detected by the divisional light-receiving elements 9 e and 9 f .
  • the signal (E ⁇ F) is 0 and has no influence on the differential push-pull signal.
  • the signal (G ⁇ H) in connection with the signals detected by the divisional light-receiving elements 9 g and 9 h.
  • FIG. 16 is a plan view showing divisional light-receiving elements of a photodetector in an optical head apparatus according to a second embodiment of the present invention and lengths (widths) in a y-direction of an interference fringe by interlayer stray light.
  • the optical head apparatus according to the second embodiment as a condition regarding positions and sizes of the divisional light-receiving elements of the photodetector 9 , a different condition is applied from the condition in the first embodiment. For this reason, FIG. 5 and FIG. 6 are also referred in the explanation of the second embodiment.
  • a division line dividing a sub-beam light-receiving unit 9 S 1 into a divisional light-receiving element 9 e and a divisional light-receiving element 9 f is disposed at a position where intensity of an interference fringe is intermediate between the strongest and the weakest positions of intensity and a division line dividing a sub-beam light-receiving unit 9 S 2 into a divisional light-receiving element 9 g and a divisional light-receiving element 9 h is disposed at a position where the intensity of the interference fringe is intermediate between the strongest and the weakest positions of intensity.
  • the sub-beam light-receiving unit 9 S 1 is divided by the first division line 9 J in an x-direction being a direction on the photodetector 9 corresponding to a tangential direction of a recording track on an optical disc 10 , that is, the divisional light-receiving element 9 e and the divisional light-receiving element 9 f which are arranged in the y-direction being orthogonal to the x-direction.
  • the sub-beam light-receiving unit 9 S 2 is divided by the second division line 9 K in the x-direction being a direction on the photodetector 9 corresponding to the tangential direction of the recording track of the optical disc 10 and includes the divisional light-receiving element 9 g and the divisional light-receiving element 9 h which are arranged in the y-direction being orthogonal to the x-direction.
  • FIG. 17A is a plan view showing the divisional light-receiving elements and an interference fringe by interlayer stray light in an example for comparison
  • FIG. 17B is a plan view showing the divisional light-receiving elements and an interference fringe by interlayer stray light in another example for comparison
  • FIG. 17C is a plan view showing the divisional light-receiving elements and an interference fringe by interlayer stray light in the second embodiment.
  • FIG. 17A shows a case that the center of a sub-beam light-receiving unit (division line) is disposed at a position where the intensity of the interference fringe is the strongest
  • FIG. 17A shows a case that the center of a sub-beam light-receiving unit (division line) is disposed at a position where the intensity of the interference fringe is the strongest
  • FIG. 17A shows a case that the center of a sub-beam light-receiving unit (division line) is disposed at a position where the
  • FIG. 17B shows a case that the center of a sub-beam light-receiving unit (division line) is disposed at a position where the intensity of the interference fringe is the weakest
  • FIG. 17C shows a case that the center of the sub-beam light-receiving unit (division line) is disposed at a position where the intensity of the interference fringe is intermediate.
  • FIG. 18A , FIG. 18B , and FIG. 18C are diagrams showing influence of the interference fringe by the interlayer stray light on a sub-beam push-pull signal, in the optical head apparatus which has the photodetector of FIG. 17A , according to the example for comparison.
  • FIG. 18A , FIG. 18B , and FIG. 18C are diagrams showing influence of the interference fringe by the interlayer stray light on a sub-beam push-pull signal, in the optical head apparatus which has the photodetector of FIG. 17A , according to the example for comparison.
  • FIG. 19A , FIG. 19B , and FIG. 19C are diagrams showing influence of the interference fringe by the interlayer stray light on a sub-beam push-pull signal in the optical head apparatus which has the photodetector of FIG. 17B , according to the other example for comparison.
  • FIG. 19A , FIG. 19B , and FIG. 19C are diagrams showing influence of the interference fringe by the interlayer stray light on a sub-beam push-pull signal in the optical head apparatus which has the photodetector of FIG. 17B , according to the other example for comparison.
  • FIG. 20A , FIG. 20B , and FIG. 20C are diagrams showing that an interference fringe by the interlayer stray light has no influence on a sub-beam push-pull signal in the optical head apparatus according to the second embodiment.
  • FIG. 20A , FIG. 20B , and FIG. 20C are diagrams showing that an interference fringe by the interlayer stray light has no influence on a sub-beam push-pull signal in the optical head apparatus according to the second embodiment.
  • the division line dividing the sub-beam light-receiving unit 9 S 1 into the divisional light-receiving element 9 e and the divisional light-receiving element 9 f is disposed at a position where the intensity of the interference fringe is intermediate between the strongest position and the weakest position of intensity and the division line dividing the sub-beam light-receiving unit 9 S 2 into the divisional light-receiving element 9 g and the divisional light-receiving element 9 h is disposed at a position where the intensity of the interference fringe is intermediate between the strongest position and the weakest position of intensity.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Mathematical Physics (AREA)
  • Optical Head (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Supporting Of Heads In Record-Carrier Devices (AREA)
US12/601,144 2007-05-30 2008-03-05 Optical head apparatus and optical disc apparatus Expired - Fee Related US7995433B2 (en)

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JP2007142895 2007-05-30
JP2007-142895 2007-05-30
PCT/JP2008/053933 WO2008146511A1 (ja) 2007-05-30 2008-03-05 光ヘッド装置及び光ディスク装置

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EP (1) EP2151823B1 (de)
JP (1) JP4481365B2 (de)
CN (1) CN101681642B (de)
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DE112012005064B4 (de) * 2011-12-05 2016-02-11 Mitsubishi Electric Corporation Optokopfeinrichtung und optische Speicherplatteneinrichtung

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WO2008146511A1 (ja) 2008-12-04
JP4481365B2 (ja) 2010-06-16
CN101681642B (zh) 2011-07-27
EP2151823B1 (de) 2012-01-11
EP2151823A1 (de) 2010-02-10
CN101681642A (zh) 2010-03-24
EP2151823A4 (de) 2010-10-20
JPWO2008146511A1 (ja) 2010-08-19
US20100149936A1 (en) 2010-06-17
ATE541288T1 (de) 2012-01-15

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